Abstract:

The defect formation in neutron irradiated SiC was investigated by means of Rutherford backscattering
spectrometry in channelling mode (RBS), optical absorption and Raman spectroscopy. The relative defect
concentration determined by RBS increases linearly with the neutron fluence without any saturation in
the investigated fluence region. The spectral dependence of the absorption coefficient a at photon energies
below 3.2 eV is independent of the neutron fluence and corresponds to that observed in low-fluence
ion implanted SiC. An increase of the defect concentration exhibits only in an increase of the absolute
value of a. For photon energies above 3.3 eV again an exponential increase of the absorption coefficient
is found but with a slope increasing with rising defect concentration. This absorption is assumed to be of
the Urbach type. Around 1.56 eV a broad absorption band is observed which is most probably caused by
divacancies VSiVC. The defects produced by the neutron irradiation of SiC result in a decrease of the peak
intensity and a shift of the position of TO and LO Raman peaks towards lower wave numbers. The latter
can be explained by tensile stress due to defects and mass increase of lattice atoms due to neutron
capturing.